1. Field of the Invention
This invention relates to a processing unit for a substrate and a processing method for a substrate.
2. Disclosure of the prior art
Processes for manufacturing semiconductor devices include steps in which semiconductors as substrates undergo processes such as oxidation, diffusion, CVD (Chemical Vapor Deposition) or the like. Vertical thermal processing units are often used for conducting the various processes. A conventional vertical thermal processing unit comprises: a carrier-transferring area where an operator or an automatic conveying mechanism holds and conveys a carrier housing semiconductor wafers, and a loading area where semiconductor wafers in the carrier are transferred to a boat as a holder for a thermal processing which is then loaded into or unloaded from a thermal processing furnace.
In such vertical thermal processing units, it is preferable for a partition (bulkhead) to be provided between the carrier-transferring area which is exposed to the atmosphere and the loading area. The partition allows the loading area to remain clean and prevents a natural oxidation film from forming on the semiconductor wafers. The loading area should also be preferably filled with an inert gas such as nitrogen. A closed-type carrier, whose entrance for semiconductor wafers can be hermetically closed by a lid, should also be preferably used in the vertical thermal processing unit in order to prevent the semiconductor wafers from being contaminated with particles.
A carrier-placing portion having an opening is arranged at the partition between the carrier-transferring area and the loading area. The opening is adapted to become in contact with the carrier on the side of the carrier-transferring area. A door is provided at the opening on the side of the loading area to open and close it. When processing the semiconductor wafers, the lid of the carrier is aligned to be in contact with the carrier-placing portion, and the door and the lid are opened to communicate the interior of the carrier with the loading area. The semiconductor wafers are then conveyed from the interior of the carrier to the boat in the loading area via the opening. The boat is then loaded in the thermal processing furnace to perform the prescribed processes on the semiconductor wafers.
Furthermore, two boats are used as below. One boat of them is placed on the lid which can be vertically elevated to open and close the opening of the thermal processing furnace. The boat is conveyed into the thermal processing furnace. While the opening of the furnace is hermetically closed with the lid and the semiconductor wafers in the boat undergo the thermal processing, other the semiconductor wafers are transferred to the other boat. This improves the throughput of the vertical thermal processing unit.
Vertical thermal processing units for semiconductor wafers having large, for example 300 mm diameters need thermal processing furnaces having large capacities and large openings. Thus, after the thermal processing, considerable heat in the furnace may leak from the opening of the furnace into the loading area while the opening of the furnace is opened, the boat in the furnace is conveyed out, the next boat is conveyed into the furnace and the opening of the furnace is closed with the lid. This may raise the temperature of the loading area and influence instruments in the loading area. In addition, the wasted energy may be so much because the interior of the thermal processing furnace has to be maintained above the predetermined temperature.
The width, the depth and the height of the vertical thermal processing unit are increased accompanying the increase of the diameter of the semiconductor wafer, for example to 300 mm. The space of the floor and the height of the ceiling are also increased for arranging the vertical thermal processing unit. These lead to the increase of the costs for manufacturing and maintaining of the vertical thermal processing unit. Therefore, there is a requirement that the vertical thermal processing unit be miniaturized as much as possible.
In order to improve the ability to process the semiconductor wafers with the vertical thermal processing unit, it is desirable that the boat-placing portion is disposed in the loading area for placing one boat to which semiconductor wafers are transferred while the thermal processing is conducted to the other boat, that the transferring mechanism is disposed in the loading area for transferring the semiconductor wafers between the boat on the boat-placing portion and the carrier at the carrier-placing portion and that the boat-conveying mechanism is disposed in the loading area for conveying the boat between the boat-placing portion and the lid. Having the trace of the boat and the occupying space of the conveying mechanism overlap is effective in miniaturizing the vertical thermal processing unit. However, in that case, there is an undesirable possibility that the boat and the transferring mechanism interference with each other.
In addition, the boat before the thermal processing may be under the lee of the other boat after the thermal processing while the two boats are conveyed between the boat-placing portion and the lid respectively. In that case, the semiconductor wafers in the boat before the thermal processing may be contaminated with particles or gases coming from the other boat after the thermal processing.
Therefore, the object of this invention is to provide a vertical thermal processing unit, which can reduce the undesirable influence caused by the heat leaking from the opening of the furnaces when the lid is taken off from the opening and the boat after the thermal processing is conveyed out.
Another object of this invention is to improve the ability to process the substrates, by making the trace of the boat and the occupying space of the transferring mechanism of the substrates overlap and by laterally evacuating the transferring mechanism from the trace of the boat when the boat is conveyed, in order to prevent the interference of the boat and the transferring mechanism.
Another object of this invention is to achieve the miniaturization of the unit by arranging a notch aligning mechanism along a vertical central line of the carrier-placing portion and by reducing the width and the depth thereof without increasing the height thereof.
Another object of this invention is to provide a boat conveying method where the contamination of the substrates is restricted when the boat is conveyed.
To achieve the above objects, this invention is characterized by a feature wherein a processing unit for a substrate comprises: a vertical thermal processing furnace having a bottom and an opening provided at the bottom, a first lid on which a boat holding substrates in vertical multistairs can be placed and which can open and close the opening of the vertical thermal processing furnace with the boat placed thereon, a boat-placing portion on which the boat and another boat can be placed, a boat conveying mechanism for conveying the two boats alternatively between the boat-placing portion and the first lid, and a second lid for hermetically closing the opening of the vertical thermal processing furnace when the first lid opens the opening but no boat passes through the opening.
According to the feature, the processing unit can effectively reduce the undesirable influence from the opening when the first lid is taken off from the opening and the boat is conveyed out, and can also reduce the wasted energy by preventing the fall of the temperature in the interior of the thermal processing furnace.
Preferably, the second lid is a shutter which can be moved vertically and horizontally with respect to an outside surface of the opening of the vertical thermal processing furnace to open and close the opening.
Preferably, the processing unit further comprises: a carrier-placing portion on which a carrier housing the substrates can be placed, and a transferring mechanism for transferring the substrates between the carrier placed on the carrier-placing portion and the boat placed on the boat-placing portion. In that case, the transference mechanism is preferably retractable in such a manner that the transferring mechanism does not interfere with the boat when the boat is conveyed by the boat conveying mechanism. In that case, the processing unit can be suitably miniaturized.
Preferably, a notch aligning mechanism is arranged along a vertical central line of the carrier-placing portion for aligning notches provided at the substrates. In that case, the width, the depth and the height of the processing unit can be effectively reduced, so that the time for transferring the substrates can be substantially reduced.
Preferably, the boat conveying mechanism includes; a first arm which has a rotational axis and a distal end and which can be vertically elevated and horizontally rotated around the rotational axis, and a second arm which is supported at the distal end in such a manner that the second arm can horizontally rotate around the distal end and which can vertically hold the boat and convey the boat in such a manner that a center of the boat passes over the rotational axis of the first arm, and the boat conveying mechanism can convey the boat in a radial direction with respect to the rotational axis of the first arm by synchronously rotating the first arm and the second arm. In that case, the space for conveying the boat can be minimized, so that the width and the depth of the processing unit can be substantially reduced.
Preferably, the transferring mechanism is movable vertically above the boat conveying mechanism.
Preferably, a ventilating unit is disposed adjacent the boat-placing portion for making a clean gas flow. In that case, the boat-placing portion has preferably a first placing portion and a second placing portion arranged between the first placing portion and the first lid, and the boat conveying mechanism is also preferably operable to convey the boat from the first placing portion to the second placing portion, from the second placing portion to the first lid, and from the first lid to the first placing portion in such a manner that the boat passes under lee of the second placing portion with respect to the clean gas flow made by the ventilating unit.
In addition, this invention is characterized by a feature wherein a processing method for a substrate by using a processing unit for the substrate comprising: a vertical thermal processing furnace having a bottom and an opening provided at the bottom, a first lid on which a boat holding substrates in vertical multistairs can be placed and which can open and close the opening of the vertical thermal processing furnace with the boat placed thereon, a boat-placing portion having a first placing portion and a second placing portion arranged between the first placing portion and the first lid, a second lid for hermetically closing the opening of the vertical thermal processing furnace when the first lid opens the opening but no boat passes through the opening, a carrier-placing portion on which a carrier housing the substrates can be placed, a transferring mechanism for transferring the substrates between the carrier placed on the carrier-placing portion and the boat placed on the boat-placing portion, a ventilating unit disposed adjacent the boat-placing portion for making a clean gas flow, and a boat conveying mechanism for conveying the boat from the first placing portion to the second placing portion, from the second placing portion to the first lid, and from the first lid to the first placing portion in such a manner that the boat passes under lee of the second placing portion with respect to the clean gas flow made by the ventilating unit, said method comprises the steps of: conveying a first boat from the first portion to the second portion by the boat conveying mechanism, conveying a second boat from the first lid to the first portion by the boat conveying mechanism in such a manner that the second boat passes under the lee of the second placing portion with respect to the clean gas flow made by the ventilating unit, and conveying the first boat from the second portion to the first lid by the boat conveying mechanism.
According to the feature, the contamination of the substrates in the boat before the thermal processing is prevented when the boat is conveyed because the boat does not pass under the lee of the other boat after the thermal processing.